Try this, it should tell you if you get anything. Plug in your guitar controller, and see if the buttons get any response:
SetBuffer BackBuffer()
While Not KeyHit(1)
Cls
Text 0,0,"Keyboard: " + GetKey()
Text 0,15,"Mouse: " + GetMouse()
Text 0,30,"JoyStick: " + GetJoy()
Flip
Wend
End